Ocurrencia, composición química y significado genético de la biotita en las rocas metamórficas de la Formación Silgará en la región suroccidental del Macizo de Santander

Abstract

The Lower Paleozoic Silgará Formation is a sequence compossed mainly by metapelitic rocks and interlayered mafic rocks that form part of the metamorphic basement that crops out in the southwestern region of the Santander Massif. The Silgará Formation of metamorphic rocks have been affected by a Barrovian type metamorphism, developing a sequence of metamorphic zones (sillimanite, staurolite-kyanite, garnet, and biotite). Metamorphism has occurred under high-temperature and medium-pressure conditions, reaching the amphibolite facies. During the prograde metamorphism of the Santander Massif metamorphic rocks, the biotite has grown in a wide range of pressure and temperature conditions, and the change in its chemical composition tends to reflect the effect of the bulk-rock chemistry rather than the grade of metamorphism.